1. Field of the Invention
The present invention relates generally to compliant mechanisms and methods of manufacturing such compliant mechanisms. More particularly, the present invention relates to multi-layered compliant mechanisms and methods of manufacturing the same.
2. Related Art
Compliant mechanisms have been developed for a variety of applications, including clutches, switches, bicycle derailleurs, and bicycle brakes. Compliant mechanisms typically include a flexible section that is allowed to bend, or moves through elastic deformation. The flexible section of the compliant mechanism can replace a pivot joint, such as a pivot pin, in the replaced device. A number of advantages are realized by compliant mechanisms, including cost reduction and increased performance. For example, compliant mechanisms can reduce the number of parts for an application or device, reduce the assembly time of such devices, and simplify the manufacturing process, thus reducing the costs associated with multiple parts. As another example, compliant mechanisms can increase precision, increase reliability, reduce wear, reduce weight, and reduce maintenance.
Although many advantages have been realized with compliant mechanisms, some disadvantages have been discovered. For example, it has been found to be difficult and/or expensive to manufacture some types or configurations of compliant mechanisms. It will be appreciated that compliant mechanisms often require tight tolerances that are difficult or expensive to manufacture. In addition, it will be appreciated that some compliant mechanisms include long, thin, flexible members with shapes designed for controlled deformation and force. The required precision and geometries contemplated are beyond what can be achieved with common casting or forging techniques. Machining and electric discharge machining (EDM) have been found to meet the requirements for tolerances, but can be overly expensive, especially when one of the goals of compliant mechanisms is to reduce the costs of a device. In addition, machining and EDM fail to meet volume and speed requirements. Stamping has been found to meet the requirement for being less-expensive, but often fails to meet tolerance requirements, thus detrimentally affecting the performance of the device.
As an example, clutches have been developed that utilize a compliant mechanism for the clutch shoe or pawl wheel. The compliant mechanism can include a rigid section or mass coupled to a flexible arm. As the clutch rotates, the rigid section or mass is caused to move outwardly by centrifugal force, either engaging or disengaging depending on the type of clutch. In addition, the flexible arm is caused to elastically deflect due to movement of the rigid section or mass. As the rotation of the clutch decreases, the strain energy stored in the flexible arm causes the rigid section or mass to move back inwardly, again disengaging or engaging depending on the type of clutch. It will be appreciated that in a compliant clutch, the flexible arm can be long and thin. In addition, it will be appreciated that the flexible arm and mass must be made to precise specifications or the operation of the clutch will be affected. For example, the thickness of the flexible arm can affect the deflection characteristics of the arm, the movement of the mass, and thus the engagement and disengagement of the clutch.
It has been recognized that it would be advantageous to develop compliant mechanisms that are easier and/or less expensive to manufacture, while maintaining the required tolerances, and thus retaining performance. In addition, it has been recognized that it would be advantageous to develop a method of manufacturing compliant mechanisms that is easier and/or less expensive, while maintaining tolerances.
The invention provides compliant mechanisms with rigid and flexible sections of integral construction. The rigid and flexible sections advantageously include a plurality of common layers stacked together. The plurality of common layers can be formed by cutting a layer of material with a thickness less than a thickness of the mechanism. The thinner layers can be quickly cut, and can be cut within the required tolerances. The rigid and flexible sections provide an integral device capable of achieving motion by elastic deformation. The flexible section is deflectable, and stores energy in the form of strain energy when deflected. The flexible section can be deflectable wholly within a plane that is parallel with the plurality of layers. Similarly, the rigid section can be movable within a plane that is parallel with the plurality of layers.
In accordance with a more detailed aspect of the present invention, the plurality of layers can each include a free portion. The free portions of the plurality of layers can be substantially unattached to free portions of adjacent layers. Thus, the free portions of the plurality of layers can be unattached and independently movable with respect to one another. For example, a clutch shoe can be formed by the rigid section, and by layers that are unattached so that the layers forming the clutch shoe can move independently with respect to one another.
Alternatively, in accordance with another more detailed aspect of the present invention, the plurality of layers can be laminated or joined together.
In accordance with another more detailed aspect of the present invention, the compliant mechanism can be a compliant overrunning clutch with centrifugal throw-out. The clutch can include a ratchet wheel and a pawl wheel rotatable with respect to one another. Ratchet teeth can be disposed on the ratchet wheel, while pawls can be coupled to the pawl wheel and engagable with the ratchet teeth. Biasing members can couple the pawl to the pawl wheel, and can bias the pawl into engagement with the ratchet tooth. The pawl can be formed by the rigid section, while the biasing member can be formed by the flexible section. Again, the plurality of layers allows the biasing member to be formed with the desired tolerances.
In accordance with another more detailed aspect of the present invention, the compliant mechanism can be a compliant floating-opposing-arm (FOA) centrifugal clutch or an s-clutch. The clutch can include a clutch shoe and drum rotatable with respect to one another. The clutch shoe can be formed at least partially by the flexible and rigid sections. The rigid section can move and the flexible section can deflect during rotation to engage an engagement surface of the drum. In addition, the plurality of layers of the clutch shoe can each include a free portion. The free portions of the plurality of layers are substantially unattached to free portions of adjacent layers of the clutch shoe. Thus, the free portions of the plurality of layers of the clutch shoe are independently movable with respect to one another.
It is of course understood that other types of compliant mechanisms can be formed in accordance with the present invention.